IMP-4, a novel metallo-beta-lactamase from nosocomial Acinetobacter spp. collected in Hong Kong between 1994 and 1998

Between 1994 and 1998, 97 imipenem-resistant Acinetobacter isolates were id entified at the Prince of Wales Hospital, Hong Kong, China, A bla(IMP) PCR product was obtained from 23 of 35 viable cultures; 12 isolates belonged to genomic DNA group 3, 8 belonged to group 2 (Acinetobacter baumannii), 2 be longed to group 13TU, and 1 belonged to group 1, The bla(IMP) homologues we re sequenced from two isolates from genomic DNA group 2 and one isolate eac h from groups 3 and 13TU, The four sequences included an identical 738-bp o pen reading frame, predicted to encode a polypeptide of 246 amino acids, wi th 95.6% homology to IMP-1 and 89.3% homology to IMP-2, The new enzyme, des ignated IMP-4, was partially purified. It had a pI of 8.0 and was strongly active against imipenem and meropenem, with V-max values 53 and 8% of that for penicillin G, respectively. Strong activity was also seen against oxyim ino-aminothiazolyl cephalosporins but not against aztreonam, Hydrolytic act ivity was inhibited by EDTA but not by clavulanate or tazobactam, Carbapene m MICs for most bla(IMP)-pnsitive isolates were 4 to 32 mug/ml, but one iso late with the intact gene was susceptible, with imipenem and meropenem MICs of 0.25 and 0.5 mug/ml, respectively. The latter isolate did not produce t he band with a pI of 8.0, and gene expression was inferred to have been los t, None of the isolates studied in detail contained extrachromosomal DNA, a nd carbapenem resistance was not transmissible to Escherichia coli. Neverth eless, the presence of bla(IMP-4) in different genomic DNA groups implies h orizontal transfer, and sequences resembling a GTTRRRY integrase-dependent recombination motif were identified in the flanking regions of bla(IMP-4).